Buggy code:
public abstract class ApacheLicenseHeaderTestCase extends TestCase { private static final String LINE_ENDING = System . getProperty ( "line.separator" ) ; private interface FileVisitor { void visitFile ( File file ) { } } private class SuffixAndIgnoreFileFilter implements FileFilter { private String [ ] suffixes ; private String [ ] ignoreFiles ; private SuffixAndIgnoreFileFilter ( String [ ] suffixes ) { } private SuffixAndIgnoreFileFilter ( String [ ] suffixes , String [ ] ignoreFiles ) { } public boolean accept ( File pathname ) { } } private class DirectoryFileFilter implements FileFilter { private String [ ] ignoreDirectory = new String [ ] { ".svn" , "target" } ; public boolean accept ( File pathname ) { } } private File baseDirectory = new File ( "" ) . getAbsoluteFile ( ) ; private String javaLicenseHeader ; private String xmlLicenseHeader ; private String propertiesLicenseHeader ; private String cssLicenseHeader ; private String velocityLicenseHeader ; private String javaScriptLicenseHeader ; private String x = ( "^(\\<\\?xml[^" + ( ApacheLicenseHeaderTestCase . LINE_ENDING ) ) + "]+).*" ; private Pattern xmlHeader = Pattern . compile ( x , Pattern . DOTALL ) ; protected String [ ] javaIgnore ; protected String [ ] htmlIgnore ; protected String [ ] propertiesIgnore ; protected String [ ] xmlIgnore ; protected String [ ] cssIgnore ; protected String [ ] velocityIgnore ; protected String [ ] javaScriptIgnore ; public ApacheLicenseHeaderTestCase ( ) { } public void testJavaFiles ( ) { } public void testHtmlFiles ( ) { } public void testPropertiesFiles ( ) { } public void testXmlFiles ( ) { } public void testCssFiles ( ) { } public void testVelocityFiles ( ) { } public void testJavaScriptFiles ( ) { } private void failIncorrectLicenceHeaders ( List < File > files ) { if ( ( files . size ( ) ) > 0 ) { StringBuffer failString = new StringBuffer ( ) ; <START_BUG> failString . append ( "The<seq2seq4repair_space>following<seq2seq4repair_space>files<seq2seq4repair_space>didn\'t<seq2seq4repair_space>have<seq2seq4repair_space>a<seq2seq4repair_space>correct<seq2seq4repair_space>license<seq2seq4repair_space>header:\n" ) ; <END_BUG> for ( File file : files ) { failString . append ( file . getAbsolutePath ( ) ) . append ( ApacheLicenseHeaderTestCase . LINE_ENDING ) ; } fail ( failString . toString ( ) ) ; } } private String extractLicenseHeader ( File file , int start , int length ) { } private boolean checkJavaHeader ( File file ) { } private boolean checkJavaScriptHeader ( File file ) { } private boolean checkXmlHeader ( File file ) { } private boolean checkPropertiesHeader ( File file ) { } private boolean checkVelocityHeader ( File file ) { } private boolean checkCssHeader ( File file ) { } private void visitFiles ( String suffix , ApacheLicenseHeaderTestCase . FileVisitor fileVisitor ) { } private void visitFiles ( String suffix , String [ ] ignoreFiles , ApacheLicenseHeaderTestCase . FileVisitor fileVisitor ) { } private void visitFiles ( String [ ] suffixes , ApacheLicenseHeaderTestCase . FileVisitor fileVisitor ) { } private void visitFiles ( String [ ] suffixes , String [ ] ignoreFiles , ApacheLicenseHeaderTestCase . FileVisitor fileVisitor ) { } private void visitDirectory ( String [ ] suffixes , String [ ] ignoreFiles , File directory , ApacheLicenseHeaderTestCase . FileVisitor fileVisitor ) { } private String loadFile ( String filename ) { } }

Fix:
failString . append ( ( ( "The<seq2seq4repair_space>following<seq2seq4repair_space>files(" + ( files . size ( ) ) ) + ")<seq2seq4repair_space>didn\'t<seq2seq4repair_space>have<seq2seq4repair_space>a<seq2seq4repair_space>correct<seq2seq4repair_space>license<seq2seq4repair_space>header:\n" ) ) ;